1. Field of Invention
The present invention relates to a method for making an aluminum nitride substrate and, more particularly, to a method for hot isostatic pressing an aluminum nitride substrate.
2. Related Prior Art
Conventional LED devices include substrates made of gallium nitride (GaN) or sapphire (Al2O3) that emits blue light. A sapphire substrate is however poor regarding thermal conductivity as its heat transfer coefficient is only 17 to 27 W/mK. Therefore, a serious problem related to heat radiation would be encountered when a large current is used to drive an LED device equipped with a sapphire substrate.
On the contrary, an aluminum nitride (“AIN”) substrate is excellent regarding thermal conductivity as its heat transfer coefficient is 170 to 230 W/mK. The thermal conductivity of an aluminum nitride substrate is seven times higher than the thermal conductivity of an aluminum oxide substrate. An aluminum nitride substrate hence lasts much longer than an aluminum oxide substrate. Accordingly, the life of an LED device equipped with an aluminum nitride substrate is about 6,000 to 7,000 hours. Moreover, an aluminum nitride substrate is highly electrically isolative, erosion-resistant and refractory, and exhibits stable physical properties. Hence, an aluminum nitride substrate is suitable for use in a high power electronic element.
To make an aluminum nitride substrate, aluminum nitride powder is made into a blank with a predetermined shape, size and strength. The forming of the blank is an important step in a process for making an aluminum nitride substrate. To form the blank, tape casting (or “doctor-blading”) may be used. The tape casting is simple but cannot be used to make a large aluminum nitride substrate. Moreover, the porosity of an aluminum nitride substrate made by the tape casting is poor so that the thermal conductivity of the aluminum nitride substrate is poor.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.